A rotary loop taker is a device that must be incorporated into all lock-stitch sewing machines. Perhaps 70 to 80 percent or more of all industrial sewing machines are of the lock-stitch type, and therefore utilize a rotary loop taker. Lock-stitch sewing machines of the type described are especially useful for sewing canvas, leather, or other heavy materials.
The conventional loop taker is precision machined of fine steel to accurate proportions and balance throughout its extent from its weighted hub to its fragile hook or "loop seizing point." It is a costly item, and a short-lived item under the heavy wear and tear that accompanies the use of a typical industrial sewing machine. Conventional loop takers have a life of only three to six months, depending on the many variables involved.
Because no one prior to the inventor in certain co-pending, commonly assigned applications (of which the earliest filed is Badillo application Ser. No. 292,036, filed Aug. 11, 1981 and now abandoned) has understood how to construct a rotary loop taker with a detachable loop seizing point that is a satisfactory device, conventional loop takers are currently constructed--as they have been for more than 60 years--with the loop seizing point formed integrally with a substantially circular frame member and with a crosswise extending frame support member as well. This of course requires that when either the loop seizing point or the initial portion of the bobbin case raceway that is an important part of the rotary loop taker has become damaged, the entire loop taker must be discarded.
The most vulnerable part of the fragile loop seizing point of a rotary loop taker is the tip. The tip can, for example, be chipped by the needle of the sewing machine, or burred by the friction that is created by the high speed revolutions of the loop taker as it picks up the thread off the needle. Since a faulty hook or loop seizing point tends to skip stitches, it must be repaired or replaced whenever its fragile loop seizing point accidentally breaks or becomes too dull through normal wear.
With the rotary loop taker of the usual type, most factories simply discard the entire device when the loop seizing point (which as pointed out is conventionally an integrally formed part of the loop taker) becomes chipped or otherwise rendered unusable. Others send the rotary loop taker to a facility that reprocesses the tip of the loop seizing point at great time loss. Either expedient is very costly.
The advantages that would be provided by a rotary loop taker with a detachable loop seizing point that could be readily removed and replaced with a new point were recognized at least six decades ago. Dickson Pat. No. 1,431,380, issued Oct. 10, 1922 on an application filed Jan. 25, 1921, attempted to provide such a loop taker. However, for several reasons the loop taker disclosed in that patent was unsatisfactory, and so far as is known was never practiced commercially.
Shortly before the Dickson patent just mentioned was issued, another patent was granted (Smith No. 1,415,268, issued May 9, 1922) that contained a good discussion of the problem in a revolving hook machine of replacing a damaged loop seizing point that is integrally formed with the rest of the rotary loop taker (page 3, lines 76-119). That patent attempted to solve the problem referred to by providing a vertically laminated hook in which the tip is secured to the rest of the hook by a set of screws and can be removed and replaced as required. (The term "vertically laminated hook" is used in this specification to refer to a loop seizing point that is laminated in layers that are parallel to the shaft of the rotary loop taker.) The device disclosed in the Smith patent was thus a detachable loop seizing point of an entirely different type from applicant's detachable hook.
Loop seizing points of vertically laminated construction unavoidably present cracks in which the needle thread loop can get caught, either in the operation of the sewing machine in a forward direction or (as is more or less common for certain purposes) in the reverse direction. Such laminated devices also present other cracks in which lint and dirt can be trapped. In addition, a vertically laminated loop seizing point is inherently weaker, and usually possesses less total mass and thus provides a less solid construction, than an integrally formed loop seizing point. Finally, some specialized hooks are so thin in the radial direction with respect to the annular supporting frame that vertical lamination is not feasible.
Despite these disadvantages, until the rotary loop takers covered by the above mentioned commonly assigned applications were invented, the approach of vertical lamination was followed, ever since the Dickson patent was issued, in all but two industrial detachable loop seizing point patents of which applicant is aware. Examples of detachable loop seizing points that are fabricated in vertically laminated form are the devices that are disclosed in the patents to Corrall et al. U.S. Pat. No. 2,002,172 issued May 21, 1935, Joseph U.S. Pat. No. 2,495,637 issued Jan. 24, 1950, Corey U.S. Pat. No. 3,140,681 issued July 14, 1964, Corey U.S. Pat. No. 3,223,060 issued Dec. 14, 1965, and Kuhar U.S. Pat. No. 3,465,700 issued Sept. 9, 1969.
The only prior art patents issued after the Dickson patent for rotary loop takers with detachable loop seizing points for use in an industrial sewing machine that do not follow the lamination approach that are known to applicant are Grabowski U.S. Pat. No. 3,139,050, issued June 30, 1964 and Thiermann German Pat. No. 933,601, issued Sept. 29, 1955.
The detachable loop seizing point disclosed in the former patent is designed to be used with an industrial sewing machine having a take-up device (ordinarily of the roller type) that is located below the bobbin case of the machine, and the complicated and expensive construction of that loop seizing point is for several reasons entirely unsuited for use with a sewing machine in which the take-up device is located above the bobbin case.
As explained below, the Thiermann rotary loop taker is unsatisfactory because, among other things, it lacks the feature of the present invention that avoids the danger of having slack needle thread loops falling partly or entirely under the bottom of the downwardly extending supporting lug of the loop seizing point, where they can be snagged and broken or cause the serious condition known as "thread lock."